BIOAUGMENTATION FOR THE IN SITU AEROBIC COMETABOLISM OF CHLORINATED SOLVENTS - Bioaugmentation for Groundwater Remediation - page 222

Table 8.2. Characteristics of Cometabolism and Their Importance to Treatment Using Indigenous
and Bioaugmented Microorganisms

Importance for the Indigenous
Process

Importance for
Bioaugmentation Aerobic Cometabolic Property

Aerobic cometabolism is often
initiated by oxygenase enzymes,
which are most often induced by
the growth substrate

Contaminant and growth
substrate usually compete for
same enzyme resulting in
competitive inhibition and the
reduction in the rates of
transformations

Competitive inhibition might be
prevented if microorganisms are
added that can grow constitutively
on non-inhibiting substrates

Cometabolic transformation
requires the presence of oxygen

Continuous addition of oxygen is
required

Injection of high cell mass for
enzyme activity may deplete the
needed oxygen

Cometabolic transformation
usually drains energy from the
microorganism

Cometabolic transformation is not
maintained for long periods after
growth substrate addition is
stopped

Microbial strains that effectively
store energy may have potential
advantages over indigenous
strains

Rates of transformation can vary
widely among different microbial
strains and different oxygenase
systems

Performance is highly dependent
on the indigenous microbial
populations stimulated under field
conditions

Cultures that effectively transform
the contaminants of interest might
be bioaugmented

Transformation product toxicity
can occur where the products
formed from the transformation
can be toxic to the cells

Provides potential advantages to
indigenous microorganisms that
consume the growth substrate
but do not transform the
contaminant(s) of interest

Cultures might be added that
effectively transform the
contaminants of interest but are
more resistant to transformation
product toxicity

Transformation yields (ratio of
mass of contaminant transformed
to mass growth substrate
consumed) can depend on the
contaminant cometabolized and
the microbial cultures

Performance depends greatly
on the microbial populations
stimulated under subsurface
conditions and can vary greatly
from site to site

Microbial cultures might be added
that have high transformation
capacities for the contaminants of
interest.

Primary growth substrates are
often not present in the
subsurface

Low indigenous microbial
populations are present resulting
in long lag times before substrate
consumption is observed

Bioaugmentation of the desired
strains would shorten the lag
period for biostimulation and
cometabolic transformation

Geochemical conditions play an
important role in the communities
stimulated and types of
oxygenases expressed

Indigenous populations
stimulated through substrate
addition may not be effective in
transforming CAHs of interest

Subsurface microbial strains that
are effective under the site's
geochemical conditions might
be added

Table 8.2 lists these and other important characteristics of the aerobic cometabolic process,
as indicated by the Moffett Test Facility and Edward AFB demonstrations as well as supporting
laboratory studies with microcosms and mixed and pure culture studies. Some of the challenges
related to aerobic cometabolism that may be overcome through bioaugmentation also are
presented in Table 8.2 as well as some of the those for which bioaugmentation is problematic.